Portable electronic devices are used for a variety of useful functions, including (i) communications devices such as mobile telephones, citizen band radios, family radio spectrum radio, and wireless internet devices, (ii) portable computing devices such as notebook computers, personal digital assistants, and calculators, (iii) military electronic devices, such as night visions devices, communications devices, precision GPS, laser targeting devices, data displays, and computing devices, and (iv) other items such as digital cameras, camcorders, global position satellite devices, portable electronic games, flashlights, radios, and audio CD/MP3 players. Further, many more such types of devices are being created all the time. In some cases, the new electronic devices have become critically important to public safety such as 911 emergency service on mobile telephones, or global position satellite devices for general aviation and marine use.
One common element in all these portable electronic devices is their need for portable electrical power. This has been traditionally solved by using assemblies of chemical batteries, either the one-time use disposable batteries (such as alkaline, zinc-air), or the multiple use rechargeable batteries (such as nickel-cadmium, nickel-metal-hydride, lead-acid, lithium-ion).
Rechargeable batteries must be near a power source to be recharged, typically, a source of 60 Hz/120V. This is generally not available in remote locations. This has made the use of field dynamo-style generators practical. Dynamo style power generators have a long history of usage. However, these generators are bulky, heavy, lowpower, single voltage, single device, fatiguing to operate, inefficient, no feedback, and/or dangerous to batteries.
The design of manually-driven dynamo generators is made difficult by the nature of the human input forces placed on the device. Humans are typically high force/low speed. But dynamos work best at low force/high speed. In hand driven dynamos, cranking forces can range up to 30 pounds. In leg driven dynamos, these forces can range up to 200 pounds. These high forces necessitate rugged, heavy mechanics. Human operating speeds are generally low at 2-3 Hz (ex: cranking revolutions per second or leg steps per second). So, in order to spin the dynamos at higher speeds, a high ratio step-up transmission needs to be included between the input motions and the spinning dynamo.
Dynamos should be operated at higher speeds to produce adequate power. In a permanent magnet dynamos such as brushless DC generators (BLDC), output power P is proportional to the dynamo spinning speed ω squared, or: Pαω2. To convert the slow input speed of the human forces to the higher speeds desired by dynamos, a step-up transmission is employed. These speed-increaser transmissions are typically single or multi-stage gear trains or belts. These transmissions are generally complicated and expensive to make because of the combined requirements for high step-up ratio, ruggedness, low friction, low acoustic noise and frequently unidirectional rotation. And consequently these transmissions are bulky, heavy and expensive.
Human-powered dynamos also operate at continually varying speeds because of the non-uniform nature of human motions. This results in constantly varying speed rotors in the dynamo that produce varying voltages and currents. However, batteries being charged or electronics being operated require carefully controlled voltages and currents. Additionally, the amount of resistance felt by the user during operation has a strong affect on how quickly the user fatigues. This resistance is also a function of the produced voltages and currents. Therefore, an electronic power control system needs to be included.
In light of the above, there is the need for an efficient portable device to produce electrical energy in the field. Additionally, there is a need for a power source that can be used to generate output current and voltages to a wide range of different electronic devices with their various battery chemistries and power needs. Moreover, there is a need for a power source that is relatively easy and efficient to use and control. Further, there is a need for a power source that reduces user fatigue. And further, there is a need for a power source that achieves high dynamo spinning speeds while remaining rugged and lightweight.